Sparking plug



Dec. 18, 195] w. B. SMiTS 2,578,754

SPARKING PLUG Filed March 9, 1949 gvwc/wIo v Paterited E3, 1951 srmmc PLUG Wytze Beye Smits, Voorburg, Netherlands; vested in the Attorney General of the United States Application March 9, 1949, Serial No. 80,492 In the Netherlands February 8, 1940 19 Claims.

This is a continuation-in-part of my copendin application Serial No. 324,224, filed March 15, 1940 (now abandoned).

This invention relates to spark plugs for use primarily with internal combustion engines, and the invention is more particularly concerned with spark plugs having spark guidance means and intended for use with the relatively low tension resulting from discharge of a condenser.

Due to the variations in the capacities of condensers under varying working conditions, it becomes desirable to construct such plugs with very small distances between the electrodes. Such small gaps, until my invention, introduced manufacturing difficulties which offset to a consid-r erable extent the advantages inherent in the use of such plugs. These difficulties are eliminated according to my invention by enhancing the electrical conductivity of the end surface of the insulation located between the electrodes and adjacent the combustion area. This is accomplished during manufacture of the plug and is done by means of the application of a layer of material of a special nature on the end surface of the insulation.

This special layer of material may either be such as to have, from the time of its application, enhanced conductivity so that it is semi-conductive, or else the layer may be such that the material comprising the layer and applied dur ing manufacture of the plug, becomes semi-conductive through the influence of the combustion taking place in the combustion area, such as the cylinder of an internal combustion engine.

Spark plugs are known wherein a carbon layer forms on the front face of the insulation owing to combustion during their operation. I specifically exclude from the scope of my invention such thin layers of carbon particles which in the course of-the operation of the spark plug are deposited on the front face of the insulator.

It is a primary object of my invention to provide a low tension spark plug for the production of sparks by utilization of condenser discharge, which plug has on the face of the insulation which separates the electrodes electrically, but connects them mechanically, a layer of material applied during manufacture of the plug. This layer either has, from the time of its application, enhanced conductivity so that it is semiconducting, or else the layer is such as to become semi-conducting through the influence of combustion in the combustion area.

These and other objects of the invention will be apparent from the following specification,

taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a side elevational view, partly in section, of a plug manufactured in accordance with my invention; and

Fig. 2 is a bottom plan view of the plug shown in Fig. 1.

In the drawings, the numeral I indicates the body of the sparking plug which acts as an outer electrode, and insulation 3 such as porcelain separates electrode l electrically from a central electrode 2. The insulation 3 connects the two electrodes mechanically and no intervening air spaces are left between the parts. As shown at 4, the insulator has on its end surface, adjacent the explosion chamber and between the electrodes, a special layer 4 of the type referred to above. and which will be discussed in greater detail present- 1y; As shown, the layer 4 does not extend be- 2 yond the front surfaces of the electrodes.

burned onto the porcelain insulator according to a well known burning treatment, as by burning on the platinum with the aid of a solution of chloride of platinum in lavender oil.

In high tension spark plugs working at 'voltages of 10,000-30,000 volts, carbon particles deposited during the operation have always been found detrimental. Attempts to keep these carbon deposits so slight that a reliable creep spark production was ensured, did not meet with success. In these spark plugs pointed or very narrow electrodes were used between which some carbon became deposited. The greatest carbon deposition obviously occurred in such plugs along the spark gap, since there was no creep spark to remove the excess of carbon. This ultimately resulted in such a fouling that the current leaked away through said deposit and no sparks could be produced, in other words, the insulating resistance became too low for the high tension.

In a low tension spark plug operating at 200 to 5000 volts and preferably in the range of 500 to 2000 volts, provisions can be made against an undue increase of the layer of carbon by choosing concentric electrodes between which successive sparks form in different places, each spark cleaning part of the surface, and being followed by a spark occurring in another place, that is, following a different path. The cleaned places have the highest resistance and remain free from spark production until sufllcient carbon has again desmarts posited there. In low tension spark plugs operated by aperiodic condenser discharges at very low tensions, circumstances may present themselves, however, whereby the spark production is unfavorably affected by insuflicient deposit of carbon.

Thus a relatively lower deposition of carbon will occur if motor fuel is used which contains a comparatively large amount of hydrogen and little carbon, while care should be taken, moreover, that in the cylinder, as little carbon as possible deposits in places other than the spark plug. Also at higher temperatures which sometimes occur in' the cylinder, the deposition of carbon from the outside i. e. carbon from the fuel mixture, will decrease.

These detrimental phenomena can be entirely eliminated if care is taken that a semi-conductive layer 4 is bonded in advance to the active surface of the insulator. Such a layer may also be formed from carbon or carbon producing materials worked up with insulating materials by coalescence, sintering or in some other suitable manner. Thus carbon may be placed in finely divided form in the known cements or enamels or other sintering or coalescing substances, and these may be applied on the insulating surface of the spark plug in a thin layer.

As substances to be incorporated into the front layer 4 to build up there a semi-conductive layer forming one single body with the insulation, organic substances may be used which split off carbon as they decompose. These are bituminous materials such as asphalt, tar, and pitch, or natural resins, which can be incorporated in the insulating material by absorption into its front layer during the manufacture thereof and decomposed during the sintering or baking process. Synthetic resins too may be used for this purpose, and as moulding powders may be mixed with powdered insulating material and, for example, after application to the front face as a paste, are sintered therewith. Likewise it is possible to use thermoplastic synthetic resins or substances such as proteins, carbohydrates (e. g. starch, sugars, cellulose) which are suitably incorporated into the front face of the insulator. These substances can be worked into the insulation to a considerable depth if the heating is applied to the front face only. This affords the additional advantage that when the front face wears away in operation new carbon particles will be liberated in the surface layer of the remaining portion of the insulator under influence of the temperature at which the plug is operated.

The semi-conductive layers to be applied on the surface of the insulation may be given any thickness, e. g. /100 inch or less, but also larger than /100 inch, provided that the resistance between the poles remains within certain limits to be specified hereinafter.

The object to be achieved is to obtain on the front face of the insulation between the poles a layer on which a creeping discharge can easily occur when a suitable electric tension is applied to the poles. It is obvious that if the resistance of the semiconductive layer should be high, the tension to be applied-which tension is preferably obtained by connecting a charged condenser to the poles of the plug with as little as possible self-induction in the circuitmust have a high value in order to produce a creep discharge, which can be disadvantageous especially because this may reduce the reliability of operation. On the other hand too low a resistance between the poles is highly undesirable since in such case the electric discharge will not occur in the form of a creep discharge over the front face of the insulator, but in the form of an electric current flowing from the one pole to the other through the semi-conductive layer. When using low tension spark plugs designed to produce sparks by means of a condenser discharge, it is suitable to keep the resistance of the semi-conductive layer 4 within limits ranging from ten ohms to a maximum of about 100,000 ohms, e. g. 20 ohms or ohms or 1000 ohms or 10,000 ohms or 50,000 ohms or 100,000 ohms. It may be of advantage to give the semiconductive layer 4 a substantial thickness, so that, if the electrodes and the semi-conductive layer should burn off, which may occur under operating conditions, the reliability of the spark plug will not decline so long as there is still a certain minimum thickness of the semi-conductive layer left. This obviously considerably prolongs the life of such a spark plug as compared with a creep spark plug provided with only a very thin semi-conductive layer 1. e. consisting of carbon deposit alone. Care must be taken that the spark plug when new, i. e. when the semi-conductive layer 4 is thickest, has a resistance which does not fall below the above-mentioned lower limit. When, owing to use, the semi-conductive layer has been burnt off so far that the resistance has risen to above the above-mentioned upper limit, the spark plug will no longer operate satisfactorily with low tension.

In this connection it should be observed, however, that when using fuels which on combustion split off carbon particles, 9. layer of carbon will deposit on the front face of the insulator separating the electrodes, which layer will maintain the semi-conductivity and will considerably retard the burning-off of the semi-conductive layer 4. In low tension spark plugs the formation of said carbon deposit is facilitated by the fact that the temperature of the front face of the spark plug is considerably lower than in high tension spark plugs, e. g. 250-300 C. as compared with about 600 C. in high tension spark plugs.

The materials to be used for the semi-conductive layers should obviously answer various requirements. They must admit of being bonded to the insulating material, and they must be sufliciently resistant to influences of temperature. In order to be capable of withstanding the strains to which they are subjected during the manufacture and the operation of the spark plug they must be relatively strong.

Instead of the finely divided metals such as platinum or the finely divided carbon spread over an insulator, it is also possible to use a continuous or discontinuous layer of substances which are semi-conductors in themselves. Such materials include, among others, silicium (silicon), titanium, germanium, zirconium, hafnium, thorium and others, various carbides such as, for example, silicon carbide, various metal oxides occurring in various stages of oxidation, such as iron oxide, nickel oxide, chromium oxide, thorium oxide, tungsten oxide and others, various spinels (these are mixed crystals of metal oxides of metals having different valencies) and furthermore various sulphides, tellurides, selenides and other suitable compounds.

In the manufacture of the insulating body 3, which, as regards its electrical insulating properties, must obviously meet much lower demands in the case or low tension creep spark plugs than in the case of the conventional high tension spark plugs, so that one has more scope in selecting the materials to be used for this purpose, it is also possible to mix finely divided conductorsor semiconductors, in the correct proportion, directly into the material close to the active front face so that after the baking or sintering treatment one single solid body is obtained.

i In addition to the above-mentioned conductors and semi-conductors, finely divided carbon may be used for the preparation of such mixtures.

Another procedure is to first bake, press or sinter the insulator 3, while still leaving a certain porosity, next to apply a solution of the semi-conductor onto the front face of the insulator so that this solution soaks into the material to some extent, but so, however, that the highest concentration is on the surface. Sintering then produces an impermeable insulat ing body, the front layer whereof has the desired semi-conductive, properties. It is also possible to apply solutions of such other substances on the preformed insulator which, owing to the sintering, provide semi-conductive properties, e. g. carbonaceous organic compounds which wholly or partly decompose at the sintering temperature so that carbon is liberated.

I wish it to be understood that the various materials and procedures disclosed herein are given in an illustrative and not a limiting sense. The invention is susceptible of variations of minor nature and it is my intent to cover by my patent all such variations falling within the scope of the invention as defined by the appended claims.

I claim:

1. A spark plug, particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and an insulating body electrically separating but mechanically connecting said electrodes, said insulating body having on its surface between said electrodes a superficial layer of finely distributed platinum burned into said surface, said layer having a resistance of from ten to one hundred thousand ohms.

2. A spark plug, particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and a porcelain insulating body elec trically separating but mechanically connecting said electrodes, said porcelain insulatin body having on its surface between said electrodes a superficial layer of finely distributed platinum burned into said surface, said layer having a resistance of from ten to one hundred thousand ohms.

3. A spark plug, particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and an insulating body electrically separating but mechanically connecting said electrodes, said insulating body having on its surface between said electrodes a tightly adhering coating of platinum having a resistance of ten to one hundred thousand ohms.

4. A spark plug, particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and an insulating body electrically separating but mechanically connecting said electrodes, said insulating body having on its surface between said electrodes a semi-conductive metal layer burned on said surface, said layer havinga resistance of from ten to one hundred thousand ohms.

5. A spark plug. particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and an insulating body electrically separating but mechanically connecting said electrodes, said body having on its surface between said electrodes 9. semi-conductive metal layer tightly adhering to said surface, said layer having a resistance of from ten to one hundred thousand ohms.

6. A spark plug according to claim 5, in which said layer is metallic, and is capable of providing a semi-conductive path for an electrical creep discharge.

7. A spark plug, particularly for the production of sparks caused by the discharge of a condenser, and comprising at least two spaced electrodes and an insulating body electrically separating but mechanically connecting said electrodes, and a front layer of semi-conductive material deposited during manufacture and onl on the portion of the front surface of said body along which sparks occur between said elec= trodes, said layer extending only as far as the front surfaces of said electrodes and forming a sin le body with the insulating body, said layer having between said electrodes a resistance of from ten to one hundred thousand ohms.

8. A spark plug according to claim 7, characterized in that the semi-conductive layer comprises elements belonging to the group consisting of carbon, silicon, titanium, germanium, zirconium, hafnium and thorium.

9. A spark plug according to claim 7, characterized in that the semi-conductive layer consists of carbides.

10. A spark plug according to claim 7, characterized in that the semi-conductive layer consists ,of metal oxides occurring in various stages of oxidation.

11. A spark plug according to claim 7 characterized in that the semi-conductive layer consists of mixed crystals of oxides of metals having different valencies.

12. A spark plug according to claim 7, characterized in that the semi-conductive layer consists of a mixture of a finely divided conductor and a non-conductor.

13. A spark plug according to claim 7, characterized in that the semi-conductive layer consists of a mixture of a finely divided semi-conductor and a non-conductor.

14. A spark plug according to claim 7, characterized in that said front layer includes an organic substance.

15. A spark plug according to claim 7, characterized in that said front layer includes a bituminous organic substance.

16'. A spark plug according to claim 7, characterized in that said front layer includes a thermoplastic synthetic resin.

17. A spark plug according to claim 7, characterized in that said front layer includes a carbohydrate.

18. A spark plug according to claim 7, said layer comprising a material which decomposes and becomes semi-conductive under the influence of the combustion process.

19. A spark plug according to claim 7, in which said layer is a. non-metallic. inorganic sub- Number stance. 2,069,951 WYTZE BEYE BMITS. 2,311,647

REFERENCES CITED 5 Number The following references are of record in the 345 676 file of this patent: 505'o85 UNITED STATES PATENTS 536,460 Number Name Date 10 3731716 1,537,903 Von Lepel May 12, 1925 .4 2,017,364 Anderson Oct. 15, 1935 Name Date Hastings Feb. 9, 193'! Doran Feb. 23, 1943 FOREIGN PATENTS Country Date Italy Jan. 13, 193'? Great Britain Apr. 18, 1939 Great Britain May 15, 1941 France Apr. '1, 1942 France Oct. 15, 1943 

